1. Field of the Invention
The present invention relates to devices for controlling circuit operations and information processing apparatuses, and it particularly relates to a device for controlling the operation modes of a given circuit and an information processing apparatus utilizing said control device.
2. Description of the Related Art
High-performance information devices are today being produced in ever-smaller sizes owing to advances in high integration technology of semiconductors. For example, every one of PDAs (personal digital assistants), notebook PCs, digital cameras and portable game terminals on the market features an enriched variety of functions that have never been seen before.
However, these devices often run on batteries and are thus subject to limitations placed by the service life of the batteries. The advances and improvements in such enhanced functions have been realized by a drastic increase in the number of transistors used, but the power consumption of a fully integrated LSI, which is a single chip combining CPU and its peripheral circuits, is not at all small. And products incorporating such sophisticated functions can never be considered satisfactory products unless such functions can be used long enough. Therefore, various techniques have been proposed in the power-saving design of information processing equipment. One example as disclosed in Reference (1) in the following Related Art List is a technology for reducing power consumption in image display, by which signal processing for image signals is stopped during horizontal and vertical mute periods when images are not outputted to and displayed on the screen.
Related Art List
(1) Japanese Patent Application Laid-Open No. Hei10-145691.
Transistors become smaller in size along with higher integration design of semiconductors. This results in smaller operating power required by such individual transistors. In the past, this tendency has been a contributing factor for a certain degree of power saving. However, a new problem is now known to develop when the gate width of a transistor is so small as to be less than 0.1 μm. That is, leakage current will occur even with circuits of static structure. Therefore, it is now necessary that this problem be addressed from a new angle or angles so as to achieve power-saving design for information devices in the near future.